Illustrated Encyclopedia of Human Anatomic Variation: Opus V: Skeletal Systems: Vertebral column

Lumbar Vertebrae

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

The first lumbar, instead of the twelfth thoracic vertebra, may present the transitional form of articular process. A lumbar rib may be present, united with the ventral surface of the transverse process or the tip of a short transverse process. The accessory rib may be elongated but is usually rudimentary. Lumbar ribs are less important clinically than cervical ribs and are usually mere rudiments An extra levator costae muscle is associated with a lumbar rib. In 559 skeletons of the Washington University collection, 8.8% had lumbar ribs (Lanier, 1944).

Occasionally, the mamillary and accessory processes are united by a bony bridge forming a foramen behind the transverse process.

The transverse process of the fourth lumbar has been reported arising from the side of the vertebral body and having no connection with either the arch or pedicle.

The fifth lumbar vertebra is subject to numerous variations of several sorts, of which the following two are of interest. In the first, the pedicles of the arch show a remarkable deviation, a complete dissolution of the continuity of the arch immediately caudal to the superior articular processes, differing from the conditions found in parts of the column. In a large series of skeletons (4,200), the incidence was about 4.2% (Roche and Rowe) .

Lumbosacral transitional vertebrae were found to vary by race. It was reported that they were present in 18% of Australian aboriginals (Mitchell), 16% of Indians (Bustami), 10% of Arabs (Bustami), 8.1% of natives of Britain (Brailsford), and 5.8% of Japanese (Toyoda). Bustami studied 340 sacra of two population groups (Arab and Indian). Of these 340 sacra, 32 or 9.4% showed evidence of unilateral sacralization and 14 or 4.1% showed bilateral sacralization. Lumbarization was no found in the 340 sacra examined. Sacralization was present to some degree in 46 specimens (13.5%). The incidence of total sacralization was 10% in Arab and was 16% in Indian population groups. Arab males had a higher incidence in all stages of sacralization while it was the Indian females that showed the higher incidence in their group.

In these specimens the anterior part consists of the vertebral body carrying the pedicles and the transverse and superior articular processes, whereas the posterior segment is composed of the lamina and the spinous and inferior articular processes. This condition is occasionally present, either unilaterally or bilaterally, in the other lumbar vertebrae and even in the thoracic vertebrae. In the second type, the fifth lumbar shows a tendency, on one or both sides, to conform to the type of the first sacral vertebra, with which it may become fused. However, there may only be four lumbar vertebrae. Failure of the union of the halves of the vertebral arch and defective laminae, in this and other regions of the column, are found in spina bifida.

Lumbosacral facets are variable. In an x-ray study of 3000 subjects, the facets faced backward in 57%, pointed inward in 12%, and were mixed or asymmetric in 31% of cases.

Variations in Lumbar Ribs

Lumbar Sacralization

Lumbar Sacralization

Lumbar Vertebra

References

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